The present invention relates to power semiconductor devices, and in particular, to lead frames in power semiconductor devices.
Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Power semiconductor devices may be used in a variety of applications, such as voltage regulators, etc. Power semiconductor devices may be packaged in various packages, such as the TO-3 package and the TO-220 package.
The TO-220 style of electronic component package may be commonly used for transistors, silicon-controlled rectifiers, and integrated circuits. TO-220 packages commonly have three leads, although units with two, four, or five leads may also be manufactured. A semiconductor die is connected to the leads and is encapsulated within the device with molding compound. One notable feature is a metal tab or heat sink with a hole, which may be used in mounting the package case to an external heat sink. Components made in TO-220 packages can handle more power than those constructed in other packages, for example, TO-92 package cases.
In some existing device packages, the leads and the heat sink are portions of a single piece that is manipulated in the manufacturing process. It is often desirable that the thickness of the heat sink is greater than the thickness of the leads, for example, to increase the thermal dissipation ability of the heat sink without making the leads unwieldy. In such a case, a dual gauge piece may be used, with the thinner gauge portion used for the leads and the thicker gauge portion used for the heat sink. However, dual gauge pieces are more difficult to manufacture, resulting in more variation between pieces and higher costs. Furthermore, the vendor base for dual gauge lead frames may be more limited than for single gauge lead frames, which may limit flexibility and reduce economies of scale.
In some other existing device packages, the semiconductor die is not attached to the same structure as the leads, but is connected to the leads via additional structures. These additional structures may result in reduced thermal performance, i.e. increased thermal resistance, junction-to-lead. These additional structures may also result in increased forward voltage drop (which equates to reduced forward safe operating area), increased power dissipation, and possible reduction of useful lifetime or decreased long-term reliability. These additional structures may also lead to increased cost due to additional manufacturing steps or reduced number of units per hour fabricated.
In some other existing device packages, the platform onto which the die is soldered is connected to the lead via a solder bond. Solder bonds add contact resistance, which results in increased forward voltage drop, which results in many of the same negative repercussions discussed in the immediately preceding paragraph. Solder bonds also represent an area of concern for quality and reliability control. Solder bonds can break or fracture and require the assembly group to maintain good process control to properly form the solder bond.
In some other existing device packages, ground pads may exist between the bond wires and the die. Such ground pads may add contact resistance. In some other existing device packages, spacers may exist between the leads and the bond pad or platform. Such spacers may inhibit thermal flow from the leads to the bond pad or platform or heat sink.
Thus, there is a need for improved semiconductor power devices. The present invention solves these and other problems by providing semiconductor power devices with a single gauge lead frame.